Number lends itself to the study of how input interacts with transferred first language (L1) knowledge to facilitate or impede second language (L2) learning. We present data from adult English speakers exposed for the first time to Indonesian, a language that expresses number through bare noun phrases, reduplication and numeral + classifier constructions. Participants were trained on each construction and subsequently tested on both familiar expressions and novel ones. Learners acquired all three constructions. We discuss our results in terms of current theories of second language acquisition. (Contains 5 tables, 2 figures and 21 notes.)